Pouch-type secondary battery, and pouch film forming device

ABSTRACT

Disclosed is a pouch-type secondary battery, which includes an electrode assembly having a positive electrode plate and a negative electrode plate disposed to face each other and a pouch case having a concave groove formed to accommodate the electrode assembly, wherein the pouch case includes a first pouch film and a second pouch film thermally fused to the first pouch film, and wherein a concave groove is formed in at least one of the first pouch film and the second pouch film, and the concave groove has a bottom surface on which the electrode assembly is placed so that the bottom surface has an area equal to or greater than an area of a reference surface that covers an opening of the concave groove.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. § 371of International Application No. PCT/KR2018/009107, filed on Aug. 9,2018, which claims priority from Korean Patent Application No.10-2017-0117852, filed on Sep. 14, 2017, the disclosures of which arehereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a pouch-type secondary battery, andmore particularly, to a pouch-type secondary battery having an increasedenergy density by reducing a dead space and an apparatus for forming apouch film that is used for the pouch-type secondary battery.

BACKGROUND ART

Recently, the interest in electric products that may be operated byusing electric energy is increasing. Accordingly, as technologydevelopment and demand for electric products are increasing, the demandfor secondary batteries as energy sources is rapidly increasing, in morediverse forms. Thus, a lot of researches on secondary batteries arebeing carried out in order to meet various demands.

Secondary batteries are classified into pouch-type secondary batteries,cylindrical secondary batteries, rectangular secondary batteries and thelike depending on the type of their exteriors, among which thepouch-type secondary battery is a secondary battery in which anelectrode assembly is included in a pouch case made of metal laminatesheets. The pouch-type secondary battery has advantages in that it maybe easily manufactured with a low manufacturing cost and also it iseasily to configure a battery pack having a large capacity by connectinga plurality of unit cells in series and/or in parallel.

For example, a single cup-type pouch-type secondary battery includes apouch case made of aluminum laminate sheets and an electrode assemblyaccommodated in the pouch case and having a plurality of stackedelectrochemical cells, each having a positive electrode, a separator anda negative electrode.

FIG. 1 is a schematic cross-sectional view showing a conventionalpouch-type secondary battery, and FIG. 2 is a diagram for illustrating aforming process in which the conventional pouch film forming apparatusforms a concave groove in a pouch film.

Referring to FIG. 1, the pouch case includes a lower pouch film 1 and anupper pouch film 2. Also, the upper pouch film 2 has a concave groove inwhich an electrode assembly 3 may be placed. The concave groove isformed at the upper pouch film 2 corresponding to the shape of theelectrode assembly 3, and the depth of the concave groove is determineddepending on the thickness of the electrode assembly 3.

Referring to FIG. 2, the conventional pouch film forming apparatusincludes a die 4 and a punch 5. A forming groove 4 a is formed at thedie 4 with a shape corresponding to a desired pouch case that is formedby using the pouch film 2. At this time, the forming groove 4 a has adepth corresponding to a depth of a concave groove to be formed in thedemanded pouch case. In addition, the punch 5 is used to place the pouchfilm 2 on the die 4 and apply a force thereto, namely press, in order toform a pouch case having a concave groove with a desired depth by usingthe pouch film 2.

However, since the diameter of the forming groove 4 a of the die 4 islarger than the diameter of the punch 5, the concave groove of the pouchfilm 2 is not formed completely in conformity with the forming groove 4a of the die. That is, due to the difference in size between the forminggroove 4 a and the punch 5 and the somewhat flexible property of thepouch film 2, in the forming process, the side surface of the pouch film2 is shaped obliquely, in a spaced state, to the sidewall of the forminggroove. Thus, if the side surface of the pouch film is formed obliquelyas above, the area of the bottom surface of the concave groove isreduced. For example, as shown in FIG. 1, assuming that the full widthof the reference surface of the concave groove is L1, the full width ofthe bottom surface is L1−2×(L2+L3), which is smaller than the referencesurface of the concave groove.

However, since the size of the electrode assembly capable of beingaccommodated in the pouch case is related to the area of the bottomsurface of the concave groove, the reduction of the area of the bottomsurface of the concave groove is disadvantageous to the energy density.Recently, a battery pack having a high energy density and a compactdesign have been actively researched and developed. In order toimplement such a battery pack, it is pointed out that an energy densityshould be improved more than a conventional technology in view of asecondary battery cell unit. Thus, it is required to increase the energydensity by reducing a dead space in the internal space of theconventional pouch-type secondary battery.

DISCLOSURE Technical Problem

The present disclosure is designed in view of the above conventionaltechnique, and the present disclosure is directed to providing apouch-type secondary battery, which is capable of increasing an energydensity by accommodating a higher capacity electrode assembly, comparedto the conventional technique, by reducing a dead space inside a pouchcase, and an apparatus for forming a pouch film used for the pouch-typesecondary battery.

Technical Solution

In one aspect of the present disclosure, there is provided a pouch-typesecondary battery, which includes an electrode assembly having apositive electrode plate and a negative electrode plate disposed to faceeach other and a pouch case having a concave groove formed toaccommodate the electrode assembly, wherein the pouch case includes afirst pouch film and a second pouch film thermally fused to the firstpouch film, and wherein a concave groove is formed in at least one ofthe first pouch film and the second pouch film, and the concave groovehas a bottom surface on which the electrode assembly is placed so thatthe bottom surface has an area equal to or greater than an area of areference surface that covers an opening of the concave groove.

The concave groove may include a first side surface region in which afull width of the concave groove is gradually decreased along the depthfrom the reference surface and a second side surface region in which thefull width of the concave groove is gradually increased from an endpoint of the first side surface region to the bottom surface.

The first side surface region may have a rounded shape.

A full width of the electrode assembly may correspond to the full widthof the concave groove at the end point of the first side surface region.

The electrode assembly may be configured so that at least one batterycell is stacked, and a full width of each of the at least one batterycell may correspond to the full width of the concave groove at a stackedlocation.

Among the at least one battery cell, the first battery cell group may bestacked in the first side surface region, and the full width of eachbattery cell of the first battery cell group may correspond to the fullwidth of the concave groove included in the first side surface region.

Among the at least one battery cell, the second battery cell group maybe stacked in the second side surface region, and the full width of eachbattery cell of the second battery cell group may correspond to the fullwidth of the concave groove included in the second side surface region

The pouch-type secondary battery may further comprise an inner filmconfigured to surround an outer circumference of the electrode assemblyaccommodated in the pouch case.

The concave groove may be formed at the first pouch film.

The first pouch film and the second pouch film may be formed using asingle film, and the second pouch film may be disposed to overlap thefirst pouch film to form a single cup-type pouch case.

In another aspect of the present disclosure, there is also provided apouch film forming apparatus for forming the pouch case having theconcave groove, the apparatus comprising: a die configured to form aforming groove with a shape corresponding to the concave groove andhaving a first die unit and a second die unit provided to relativelymove in a horizontal direction; and a punch configured to move into orout of the forming groove and provided to closely adhere a concavegroove target of the pouch film to a surface of the forming groove bymeans of air pressure before a forming process.

A top surface of the second die unit on which the pouch film is placedmay be relatively wider than the first die unit.

The punch may have a plurality of air discharge holes capable ofinjecting a compressed air outwards.

The punch may be made of soft material that is shrinkable and expandableaccording to the injection of air.

Advantageous Effects

According to an embodiment of the present disclosure, it is possible toprovide a pouch-type secondary battery capable of increasing an energydensity by accommodating a higher capacity electrode assembly byreducing a dead space inside the pouch case.

According to another embodiment of the present disclosure, it ispossible to provide a pouch film forming apparatus capable of forming apouch film having a concave groove whose bottom surface on which theelectrode assembly may be placed is at least equal to or greater than areference surface that covers an opening of the concave groove of thepouch film.

DESCRIPTION OF DRAWINGS

The accompanying drawings illustrate a preferred embodiment of thepresent disclosure and together with the foregoing disclosure, serve toprovide further understanding of the technical features of the presentdisclosure, and thus, the present disclosure is not construed as beinglimited to the drawing.

FIG. 1 is a schematic cross-sectional view showing a conventionalpouch-type secondary battery.

FIG. 2 is a diagram for illustrating a forming process in which theconventional pouch film forming apparatus forms a concave groove in apouch film.

FIG. 3 is a perspective view schematically showing a pouch caseaccording to an embodiment of the present disclosure.

FIG. 4 is a schematic cross-sectional view showing the pouch case andthe electrode assembly of FIG. 3.

FIG. 5 is a schematic cross-sectional view showing that the electrodeassembly is accommodated in the pouch case of FIG. 3 and then the pouchcase is sealed.

FIG. 6 is a schematic cross-sectional view showing the pouch-typesecondary battery of FIG. 5 that is vertically reversed after thesealing portion is folded.

FIG. 7 is a perspective view showing an electrode assembly of apouch-type secondary battery according to another embodiment of thepresent disclosure.

FIG. 8 is a schematic cross-sectioned view showing the pouch-typesecondary battery according to another embodiment of the presentdisclosure.

FIG. 9 is a perspective view showing an electrode assembly of apouch-type secondary battery according to still another embodiment ofthe present disclosure.

FIG. 10 is a schematic cross-sectioned view showing the pouch-typesecondary battery according to still another embodiment of the presentdisclosure.

FIGS. 11 to 14 are diagrams for illustrating a forming process in whichthe pouch film forming apparatus according to an embodiment of thepresent disclosure forms a concave groove in a pouch film.

FIGS. 15 and 16 are diagrams for illustrating a forming process in whichthe pouch film forming apparatus according to another embodiment of thepresent disclosure forms a concave groove in the pouch film.

BEST MODE

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentdisclosure on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation.

Therefore, the description proposed herein is just a preferable examplefor the purpose of illustrations only, not intended to limit the scopeof the disclosure, so it should be understood that other equivalents andmodifications could be made thereto without departing from the scope ofthe disclosure.

Since the embodiments disclosed herein are provided for more perfectexplanation of the present disclosure, the shape, size and the like ofcomponents may be exaggerated, omitted or simplified in the drawings forbetter understanding. Thus, the size and ratio of components in thedrawings do not wholly reflect the actual size and ratio.

FIG. 3 is a perspective view schematically showing a pouch caseaccording to an embodiment of the present disclosure, and FIG. 4 is aschematic cross-sectional view showing the pouch case and the electrodeassembly of FIG. 3.

Referring to FIGS. 3 and 4, a pouch-type secondary battery according toan embodiment of the present disclosure includes an electrode assembly10, and a pouch case 20 composed of a first pouch film 30 having aconcave groove 31 capable of accommodating the electrode assembly 10 anda second pouch film 40 capable of being thermally fused to the firstpouch film 30 in a vertical direction.

As will be explained in more detail below, the pouch case 20 accordingto the present disclosure has the same full width as a conventionalpouch case 20, but may further ensure an internal space in which theelectrode assembly 10 may be effectively accommodated. Thus, based onthe same specification, the pouch-type secondary battery according tothe present disclosure has a higher energy density because it mayaccommodate the electrode assembly 10 with a larger capacity incomparison to a conventional pouch-type secondary battery. If thepouch-type secondary batteries according to the present disclosure areused, it is possible to design a more compact battery pack, compared toa conventional one.

First, the electrode assembly 10 of the pouch-type secondary batteryaccording to the present disclosure will be briefly described. Thoughnot shown in detail for the sake of convenience of illustration, theelectrode assembly 10 may include a positive electrode plate and anegative electrode plate which are disposed to face each other. Thepositive electrode plate and the negative electrode plate are formed bycoating a current collector with active material slurry. The slurry isusually formed by stirring a solvent in which a granular activematerial, an auxiliary conductor, a binder, a plasticizer and the likeare added.

The positive electrode plate and the negative electrode plate areprovided in a plate form and are disposed to be spaced apart so thattheir plates face each other. A separator is interposed between thepositive electrode plate and the negative electrode plate so that thepositive electrode plate and the negative electrode plate are not indirect contact with each other. The separator has a porous structure sothat the positive electrode plate and the negative electrode plate areblocked not to be short-circuited allow charge transfer during chargingor discharging.

An electrode lead may be attached to the electrode assembly 10, and theelectrode lead may be exposed out of the pouch case 20 to serve as anelectrode terminal that may be electrically connected to anothersecondary battery or an external device. The electrode lead may becoupled with an electrode tab that is directly connected to theelectrode assembly 10. Here, at least one positive electrode tab and atleast one negative electrode tab may be coupled with a positiveelectrode lead 11 and a negative electrode lead 12, respectively.

The pouch case 20 may include an outer insulating layer made of apolymer material, an inner adhesive layer, and a metal layer interposedbetween the outer insulating layer and the inner adhesive layer. Here,the metal layer may be made of any one selected from the groupconsisting of iron, carbon, an alloy of chromium and manganese, an alloyof iron, chromium and nickel, and aluminum or equivalents thereof, andthe aluminum metal foil is widely used. The pouch case 20 protects theelectrode assembly 10 and internal components such as the electrolyte,and performs the function of complementing electrochemical properties ofthe electrode assembly 10 and the electrolyte and dissipating heattherefrom.

The pouch case 20 of this embodiment is a single cup-type pouch case 20and is composed of a first pouch film 30 and a second pouch film 40whose one edges are connected to each other as shown in FIG. 3. Inaddition, the first pouch film 30 has a concave groove 31 so that theelectrode assembly 10 may be placed therein. The concave groove 31 ofthe first pouch film 30 may be formed to have a depth corresponding tothe thickness of the electrode assembly 10 by means of a formingprocess.

In this embodiment, the concave groove 31 is formed only in the firstpouch film 30, but a concave groove 31 of the same shape may also beformed in the second pouch film 40. That is, by forming the concavegroove 31 in both the first pouch film 30 and the second pouch film 40,it is possible to accommodate a thicker electrode assembly 10 than theelectrode assembly 10 of this embodiment. In addition, the first pouchfilm 30 and the second pouch film 40 may be separately prepared and bethermally fused in a vertical direction.

FIG. 5 is a schematic cross-sectional view showing that the electrodeassembly is accommodated in the pouch case of FIG. 3 and then the pouchcase is sealed, and FIG. 6 is a schematic cross-sectional view showingthe pouch-type secondary battery of FIG. 5 that is vertically reversedafter the sealing portion is folded.

Referring to FIGS. 4 to 6, a bottom surface 36 of the concave groove 31on which the electrode assembly 10 is capable of being placed may havean area equal to or greater than an area of a reference surface 33 thatcovers an opening of the concave groove 31. Here, the reference surface33 may be understood as a surface corresponding to one surface of thesecond pouch film 40 that covers the opening of the concave groove 31.

For reference, the single cup-type pouch case 20 has a sealing portion Sformed by disposing the second pouch film 40 to overlap the first pouchfilm 30 and then thermally fusing their terrace portions, namely theirouter rim portions that overlap each other. As shown in FIG. 6, thesealing portion S may be folded toward the electrode assembly 10. Atthis time, the full width of the pouch-type secondary battery may beapproximately equal to the full width of the reference surface 33.

Referring to FIGS. 4 and 5 again, the concave groove 31 has a first sidesurface region 34 in which the full width of the concave groove 31 isgradually decreased along the depth from the reference surface 33 and asecond side surface region 35 in which the full width of the concavegroove 31 is gradually increased from an end point of the first sidesurface region 34 to the bottom surface 36 of the concave groove 31 thatis a deepest place.

The first side surface region 34 has a rounded shape. In other words,the first side surface region 34 is a portion that forms a top of theconcave groove 31, and may be concavely recessed toward the electrodeassembly 10 when the pouch case 20 is viewed from the side.

By providing the first side surface region 34 in the concave groove 31of the first pouch film 30, it is possible to prevent stress fromconcentrating on the corresponding portion. In other words, if the pouchfilm reaches the softness limit of the materials of the metal layer andthe insulating layer during the foaming process, the pouch film may betorn without being able to withstand the stress caused by the foaming.In particular, a top edge of the concave groove 31 is vulnerable tostress even after forming. Thus, in the present disclosure, by providingthe first side surface region 34 formed in a rounded shape, the stressmay not concentrate but be dispersed at the top edge of the concavegroove 31. The first side surface region 34 may correspond to acurvature R of an edge portion of a die 100 of a pouch film formingapparatus, explained later.

Meanwhile, it is desirable that the first side surface region 34 isrelatively shorter compared to the second side surface region 35 in viewof the space efficiency inside the pouch case 20. In this embodiment,the first side surface region 34 is formed in the concave groove 31, butthe first side surface region 34 may be not formed at the concave groove31. That is, the concave groove 31 may form the second side surfaceregion 35 having an increasing full width directly from the referencesurface 33, without the first side surface region 34.

The second side surface region 35 may be a region that determines thedepth of the concave groove 31. That is, the second side surface region35 may correspond approximately to the thickness of the electrodeassembly 10. The second side surface region 35 is formed so that thefull width of the concave groove 31 is gradually increased along thedepth of the concave groove 31, namely along a depression direction. Theend point of the second side surface region 35 is connected to fouredges of the bottom surface 36 of the concave groove 31. Thus, the widthof the bottom surface 36 of the concave groove 31 may be determined bythe slope or length of the second side surface region 35. In thisembodiment, the second side surface region 35 is formed so that thebottom surface 36 of the concave groove 31 is identical to the referencesurface 33 of the concave groove 31.

If the bottom surface 36 of the concave groove 31 is equal to thereference surface 33 of the concave groove 31 as in the presentdisclosure, it is possible that an electrode assembly 10, which islarger than the conventional electrode assembly 10 (see FIG. 1), isplaced in the concave groove 31.

More specifically, referring to FIGS. 1 and 5, a conventional pouch-typesecondary battery and a pouch-type secondary battery according to thepresent disclosure having the same full width of L1 will be compared. Inthe conventional pouch-type secondary battery, the full width (L1) isthe sum of a total width (T1) of the conventional electrode assembly 10,a full width (2×L3) of a dead space and a full width (2×L2) of thestress relaxed region. Meanwhile, in the pouch-type secondary batteryaccording to the present disclosure, the full width (L1) is the sum of afull width (T2) of the electrode assembly 10 and a full width (2×L2) ofthe first side surface region 34.

In summary, the following relation is established between theconventional pouch-type secondary battery and the pouch-type secondarybattery according to an embodiment of the present disclosure.L1=T1+(2×L3)+(2×L2)=(T2)+(2×L2)

Thus, in the present disclosure, it may be understood that even thoughthe full width of the pouch case is the same, an electrode assembly 10larger than the electrode assembly 10 capable of being accommodated inthe conventional pouch case 20 may be accommodated.

As described above, the pouch case 20 according to the presentdisclosure is formed such that the bottom surface 36 of the concavegroove 31 is formed identical to the reference surface 33, and thus itis possible that the electrode assembly 10 having a full widthcorresponding to the full width of the concave groove 31 at least at theend point of the first side surface region 34 may be accommodated, whichmay increase the energy density of the pouch-type secondary battery.

Hereinafter, a pouch-type secondary battery according to anotherembodiment of the present disclosure will be described.

FIG. 7 is a perspective view showing an electrode assembly of apouch-type secondary battery according to another embodiment of thepresent disclosure, and FIG. 8 is a schematic cross-sectioned viewshowing the pouch-type secondary battery according to another embodimentof the present disclosure.

Referring to FIGS. 7 and 8, the pouch-type secondary battery accordingto another embodiment of the present disclosure includes an electrodeassembly 10′ and a pouch case 20 composed of a first pouch film 30having a concave groove 31 capable of accommodating the electrodeassembly 10′ and a second pouch film 40 capable of being thermally (H)fused to the first pouch film 30 in a vertical direction.

The pouch-type secondary battery according to another embodiment of thepresent disclosure is different from the pouch-type secondary batteryaccording to the former embodiment of the present disclosure just in theconfiguration and shape of the electrode assembly 10′, and shapes androles of other components may be identical.

In an electrode assembly 10′ of the pouch-type secondary batteryaccording to another embodiment of the present disclosure, at least onebattery cell 10-1, . . . , 10-4 may be stacked. At this time, at leastone battery cell 10-1, . . . , 10-4 may have different full widths. Inmore detail, the full width of each of the at least one battery cell10-1, . . . , 10-4 may correspond to the full width of the concavegroove 31 at a location where each of the at least one battery cell10-1, . . . , 10-4 is stacked, when at least one battery cell 10-1, . .. , 10-4 is accommodated in the concave groove 31 of the pouch case 20.

For example, among the at least one battery cell 10-1, . . . , 10-4, thebattery cell 10-4 stacked at a location contacting the bottom surface 36of the concave groove 31 may be formed to have a full width identical tothe longest full width of the concave groove 31.

In other words, each of the at least one battery cell 10-1, . . . , 10-4may be formed to have a full width elongated as long as possible so thatboth ends thereof are in contact with the concave groove 31 at a locatedaccommodated and stacked in the concave groove 31. By doing so, whenbeing accommodated in the concave groove 31, both ends of the at leastone battery cell 10-1, . . . , 10-4 may be partially in contact with theinner surface of the concave groove 31.

The at least one battery cell 10-1, . . . , 10-4 may be classified intoa first battery cell group 10 a stacked in the first side surface region34 in which the full width of the concave groove 31 is graduallydecreased along the depth from the reference surface 33 and a secondbattery cell group 10 b stacked in the second side surface region 35 inwhich the full width of the concave groove 31 is gradually increasedfrom an end point of the first side surface region 34 to the bottomsurface 36.

For example, as shown in FIG. 8, the first battery cell group 10 a mayinclude a single battery cell 10-1, and the second battery cell group 10b may include three battery cells 10-2, . . . , 10-4.

The full width of the battery cell 10-1 of the first battery cell group10 a may correspond to the full width of the concave groove 31 includedin the first side surface region 34.

In addition, the full widths of the battery cells 10-2, . . . , 10-4 ofthe second battery cell group 10 b may correspond to the full width ofthe concave groove 31 included in the second side surface region 35.

In other words, as the at least one battery cell 10-1, . . . , 10-4included in the first battery cell group 10 a and the second batterycell group 10 b have different full widths, the side surface of theelectrode assembly 10′ may be formed in a step shape corresponding tothe full width of the concave groove 31.

Accordingly, the side surface of the electrode assembly 10′ may have astep structure with a stair shape.

In the pouch-type secondary battery according to another embodiment ofthe present disclosure, since the full widths of the at least onebattery cell 10-1, . . . , 10-4 are extended corresponding to the fullwidth of the concave groove 31 that is increased or decreased from thereference surface 33 to the bottom surface 36, the at least one batterycell 10-1, . . . , 10-4 may have different volumes to be as close to thevolume of the concave groove 31 as possible.

By doing so, by reducing the empty space in the concave groove 31 wherea battery is not accommodated as much as possible, the energy density ofthe pouch-type secondary battery may be improved.

Meanwhile, even though it has been described that four battery cells10-1, . . . , 10-4 are stacked in the electrode assembly 10′ depicted inFIGS. 7 and 8, it is also possible that the battery cells 10-1, . . . ,10-4 are designed to have a smaller thickness and then five or morebattery cells are stacked.

In other words, as a plurality of battery cells are stacked in theelectrode assembly 10′ to minimize the empty space in the concave groove31, the distance between both ends of each battery cell and the sidesurface of the inside of the concave groove 31 is reduced so thatbattery cells are filled in the space of the concave groove 31 as muchas possible.

Hereinafter, a pouch-type secondary battery according to still anotherembodiment of the present disclosure will be described.

FIG. 9 is a perspective view showing an electrode assembly of apouch-type secondary battery according to still another embodiment ofthe present disclosure, and FIG. 10 is a schematic cross-sectioned viewshowing the pouch-type secondary battery according to still anotherembodiment of the present disclosure.

Referring to FIGS. 9 and 10, in the pouch-type secondary batteryaccording to still another embodiment of the present disclosure, atleast one battery cell 10-1, . . . , 10-4 may be stacked in theelectrode assembly 10′, and an outer circumference of the at least onebattery cell 10-1, . . . , 10-4 may be surrounded by an inner film 50.

In more detail, the inner film 50 may have a tube shape as shown in FIG.9 to surround the outer circumference of the at least one battery cell10-1, . . . , 10-4 as the at least one battery cell 10-1, . . . , 10-4is inserted therein.

The inner film 50 may be a thermally shrinkage tube that may shrink whenheat (H) is applied thereto. By heating after the at least one batterycell 10-1, . . . , 10-4 are inserted in the inner film 50 as describedabove, the inner film 50 may surround the outer circumference of the atleast one battery cell 10-1, . . . , 10-4 to fit the outer shapethereof.

In other words, if heat (H) is applied, the inner film 50 may shrinkwhile surrounding the outer circumference of the at least one batterycell 10-1, . . . , 10-4 inserted therein into a shape corresponding tothe step structure thereof.

Accordingly, when the at least one battery cell 10-1, . . . , 10-4having different full widths are stacked and accommodated in the concavegroove 31, the inner film 50 may support the side surface of the atleast one battery cell 10-1, . . . , 10-4 so that the at least onebattery cell 10-1, . . . , 10-4 does not move inside the concave groove31.

Meanwhile, even though it has been described that four battery cells10-1, . . . , 10-4 are stacked in the electrode assembly 10′ depicted inFIGS. 9 and 10, it is also possible that the battery cells 10-1, . . . ,10-4 are designed to have a smaller thickness and then five or morebattery cells are stacked.

In other words, as a plurality of battery cells are stacked in theelectrode assembly 10′ to minimize the empty space in the concave groove31, the distance between both ends of each battery cell and the sidesurface of the inside of the concave groove 31 is reduced so thatbattery cells are filled in the space of the concave groove 31 as muchas possible.

Hereinafter, a pouch film forming apparatus for forming the pouch case20 will be described with reference to FIGS. 11 to 14.

FIGS. 11 to 14 are diagrams for illustrating a forming process in whichthe pouch film forming apparatus according to an embodiment of thepresent disclosure forms the concave groove 31 in a pouch film.

A pouch film forming apparatus according to an embodiment of the presentdisclosure includes a die 100 composed of a first die unit 120 and asecond die unit 130, which are provided to be relatively movable in ahorizontal direction to form the forming groove 110 with a shapecorresponding to the concave groove 31, and a punch 200 configured tomove into or out of the forming groove 110 and to closely adhere aconcave groove target 30 a of the pouch film to the surface of theforming groove 110 by means of air pressure before the forming process.

The die 100 is a metallic structure having the forming groove 110 withthe same shape as the concave groove 31 of the pouch film and serves asa mold. In particular, the first die unit 120 and the second die unit130 constituting the die 100 according to the present disclosure areprovided to be relatively movable in the horizontal direction.Alternatively, it is also possible that any one of the first die unit120 and the second die unit 130 is moved with respect to the other orboth of them are horizontally moved relative to each other.

The first die unit 120 and/or the second die unit 130 may be movedrelative to each other using, for example, a linear motion (LM) guide(not shown) as a moving means of the die 100. Also, any driving devicemay be used as long as it is able to move the first die unit 120 and thesecond die unit 130 relative to each other.

In the present disclosure, the first die unit 120 and the second dieunit 130 are relatively moved in the horizontal direction, so that thepouch film may be easily pulled out from the forming groove 110 of thedie 100 while maintaining its formed shape after the forming process.

In addition, the top surface of the second die unit 130 on which thepouch film is placed may be relatively larger than the first die unit120. In the single cup-type pouch case 20, the first pouch film 30 andthe second pouch film 40 are integrally formed so that their one sideedges are connected to each other. For better manufacture of the singlecup-type pouch case 20, the second die unit 130 may be made wider thanthe top surface of the first die unit 120 to support the second pouchfilm 40 when the concave groove 31 is formed in the first pouch film 30.

The punch 200 according to this embodiment is provided to be movable upand down with respect to the forming groove 110 of the die 100 so thatthe concave groove target 30 a of the pouch film placed on the die 100is pressed into the forming groove 110. In particular, in thisembodiment, a plurality of air discharge holes 210 for spraying acompressed air from the inside to the outside are provided at a lowerend of the punch 200, so that the pouch film may be closely adhered tothe surface of the forming groove 110 by air pressure.

Meanwhile, a corner portion of the forming groove 110 of the die 100 anda corner portion of the punch 200 are rounded to have a predeterminedcurvature, so that the stress applied to the pouch film during theforming process may be reduced to prevent the pouch film from beingdamaged.

Hereinafter, the forming process of the pouch case 20 will be brieflydescribed.

As shown in FIGS. 11 and 12, a pouch film is placed on the die 100, andthe concave groove target 30 a of the pouch film is pressed using thepunch 200. At this time, the concave groove target 30 a of the pouchfilm is brought into contact with the bottom surface 36 of the forminggroove 110.

Then, as shown in FIG. 13, an air compressor (not shown) is operated todischarge a compressed air out of the punch 200 through the airdischarge holes 210. Accordingly, the pouch film may be closely adheredto the side surface of the forming groove 110. If the pouch film iscompletely formed, the air compressor stops operating.

After that, as shown in FIG. 14, the punch 200 is removed from the die100, and then the first die unit 120 and the second die unit 130 aremoved relative to each other such that the formed pouch film may besafely removed from the die 100. Then, the pouch film is completelyremoved from the die 100 to complete the forming process.

According to the pouch film forming apparatus configured as above, thepouch film may be mechanically formed such that the bottom surface 36 ofthe concave groove 31 has an area equal to or greater than an area ofthe reference surface 33 of the pouch film.

Hereinafter, a pouch film forming apparatus according to anotherembodiment of the present disclosure will be described.

FIGS. 15 and 16 are diagrams for illustrating a forming process in whichthe pouch film forming apparatus according to another embodiment of thepresent disclosure forms a concave groove in the pouch film. The samereference numerals as those in the former embodiment denote the samecomponents, and the same components will not be described in detail.

The punch 200 of this embodiment is made of a flexible material capableof shrinking or expanding as air is injected. For example, in thisembodiment, the punch 200 is an air bag made of rubber into which airmay be injected, and the air bag may be inflated when the air isinjected therein.

Thus, as shown in FIG. 15, the pouch film is pushed into the forminggroove 110 by pressing the concave groove target 30 a using the punch200 into which a predetermined amount of air is injected. After that, asshown in FIG. 16, if air is injected again in a state where the punch200 is inserted into the forming groove 110, the punch 200 expandsaccording to the shape of the forming groove 110, so that the concavegroove target 30 a of the pouch film is closely adhered to the surfaceof the forming groove 110.

After that, the air is taken out to shrink the punch 200, and then thefirst die unit 120 and the second die unit 130 are moved relative toeach other to pull the pouch film out of the forming groove 110.

In the pouch film forming apparatus according to another embodiment ofthe present disclosure, the punch 200 is made of a soft material and isthus softer than the punch 200 of the former embodiment that is made ofa hard material. Thus, the pouch film is less likely to be damagedduring the foaming process. In addition, since the punch 200 made of asoft material inflates inside the forming groove 110 to press the entireconcave groove target 30 a of the pouch film, the concave groove target30 a is more closely adhered to the forming groove 110 of the pouchfilm, thereby further improving the forming completeness.

The present disclosure has been described in detail. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the disclosure, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the disclosure will become apparent to those skilledin the art from this detailed description.

Meanwhile, when the terms indicating up, down, left, right, front andrear directions are used in the specification, it is obvious to thoseskilled in the art that these merely represent relative locations forconvenience in explanation and may vary based on a location of anobserver or a shape in which an object is placed.

What is claimed is:
 1. A pouch-type secondary battery, which includes anelectrode assembly having a positive electrode plate and a negativeelectrode plate disposed to face each other and a pouch case having aconcave groove formed to accommodate the electrode assembly, wherein thepouch case includes a first pouch film and a second pouch film thermallyfused to the first pouch film, and wherein the concave groove is formedin at least one of the first pouch film and the second pouch film, andthe concave groove has a bottom surface on which the electrode assemblyis placed so that the bottom surface has an area equal to or greaterthan an area of a reference surface that covers an opening of theconcave groove, wherein the concave groove includes a first side surfaceregion extending from the reference surface and a second side surfaceregion extending from an end point of the first side surface region tothe bottom surface, wherein the electrode assembly includes a firstbattery cell group stacked in the first side surface region and a secondbattery cell group stacked in the second side surface region, a firstfull width of each battery cell of the first battery cell groupcorresponds to a first full width of the concave groove included in thefirst side surface region, and a second full width of each battery cellof the second battery cell group corresponds to a second full width ofthe concave groove included in the second side surface region, whereinthe second full width of each battery cell of the second battery cellgroup is greater than the first full width of each battery cell of thefirst battery cell group, and wherein the end point of the first sidesurface region is closer to the reference surface than to the bottomsurface, such that a height of the second side surface region in a depthdirection from the reference surface is greater than a height of thefirst side surface region in the depth direction.
 2. The pouch-typesecondary battery according to claim 1, further comprising: an innerfilm configured to surround an outer circumference of the electrodeassembly accommodated in the pouch case.
 3. The pouch-type secondarybattery according to claim 1, wherein the concave groove is formed atthe first pouch film.
 4. The pouch-type secondary battery according toclaim 3, wherein the first pouch film and the second pouch film areformed using a single film, and the second pouch film is disposed tooverlap the first pouch film to form a single cup-type pouch case. 5.The pouch-type secondary battery according to claim 1, wherein in thefirst side surface region the first full width of the concave groove isgradually decreased in a depth direction from the reference surface andin the second side surface region the second full width of the concavegroove is gradually increased from the end point of the first sidesurface region in the depth direction to the bottom surface.
 6. Thepouch-type secondary battery according to claim 5, wherein the firstside surface region has a rounded shape.
 7. The pouch-type secondarybattery according to claim 5, wherein a full width of the electrodeassembly corresponds to the first full width of the concave groove atthe end point of the first side surface region.